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BIOC33/34 Lec 11.docx

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Biological Sciences
Stephen Reid

BIOC34 Lec 11  Pulmonary function tests o Used to diagnose lung diseases o Alveolar ventilation - calculating amount of air going into alveoli  Lung function tests - Spirometry o Done with electronic machines o Standard spirometer used to be a drum in water and person breathes in and out  Drum connected to a pen which makes recordings  Lung volumes o Can sum these lung volumes into lung capacities -give an indication of how well lung is functioning o Tidal volume (Vt) - amount of air on breath by breath basis  On average, Vt is 500ml per breath - average is 12 breaths per minute o If taking a maximal inspiration, amount of air breathed in above and beyond Vt that can maximally be taken in  Inspiratory reserve volume (IRV) o Amount of air that can be expired following normal Vt is referred to as Expiratory reserve volume (ERV) o Exhaling as much as possible, there is still air in lungs  Residual volume (RV) o Can add these volumes to create different lung capacities  Lung capacities o o 1. Inspiratory capacity (IC) = maximum amount of air that we can inspire after a normal expiration  IC = Vt + IRV o 2. Taking maximal inspiration and then breathe out as much as you can to maximum expiratory capacity = vital capacity (VC)  VC = IRV + Vt + ERV  When doing pulmonary function tests, it is called forced vital capacity o 3. Amount of air in lungs after normal tidal expiration = functional residual capacity (FRC)  Expiratory reserve + residual volume = functional residual capacity (FRC = ERV + RV)  In-between inspiration and expiration  Presence of this air exists because lung recoil in and chest recoil out o 4. Total lung capacity (TLC) = sum of everything  (TLC = IRV +Vt + ERV + RV)  Lung volumes and capacities o IC = Vt + IRV o Can measure these variables to see if have lung diseases o Important one = vital capacity (VC)  Obstructive or restrictive lung diseases o Thick lines = where problem exists o Obstructive disease = problem exhaling  Usually some kind of blockage/airway obstruction; something is hindering air going out  Harder to expire  Increase lung resistance (lungs over-inflate) • Asthma, bronchitis, problem with narrowed trachea o Restrictive disease = problem with inhaling  Damage to the lungs, chest wall or pleura  Harder to inspire (inflate lungs)  Decrease lung compliance - cannot inflate properly; lungs have become stiffer • Asbestosis, fibrosis (fibres into lung tissue making them harder)  Pulmonary function tests (forced vital capacity) o When doing these tests, hooked up to a machine and asked to breathe in and breathe out as much as possible and quickly  Forced vital capacity - breathing out as hard and quickly as you can  Vital capacity after first second is a key variable o VC can change or is different in different people o FVC is determined by:  1. Strength of respiratory muscles, chest, diaphragm, etc. will have an effect  more muscular person can push air out much more quickly than someone with weaker lungs and chest muscles  2. Airway resistance - Can change during disease states (asthma, bronchitis)  E.g. narrowed airway due to inflammation or mucous build-up  3. Lung size - can be different or damaged (tuberculosis)  4. Elastic properties of the lung o Can have obstructive disease with restrictive disease origins o Taking a maximal inspiration and breathing out as much as possible  Forced expiratory volume o Forced Expiratory Volume:Amount of forced vital capacity a person can breathe out in a certain amount of time o Can look at forced expiratory volume in seconds after one expires, but usually FEV 1  amount of vital capacity that can be exhaled in 1 second o Both FVC and FEV are going to decrease when there is obstructive and restrictive lung diseases - change in a way that the ratio of the 2 is different depending on type of disease  Pulmonary function tests (FVC and FEV) o Exhale over a 5 second period - take a maximal inspiration in and fill lungs then breathe air out as quickly as possible o Obstructive and restrictive: FVC and FEV1 are low o If ratio between FEV1 to FVC…  Is low (<0.8) , this indicates an obstructive disease  Is normal or slightly higher, this indicates a restrictive lung disease  FVC and FEV o On left = normal  FVC = 5L, FEV1 = 4L  Within first second, 4/5 L are exhaled, therefore ratio = 0.8 o In both  FVC and FRC are lower  Respiratory volume decreases o Obstructive  FEV1 = 1.2 L, FVC = 3.0L  Ratio = 0.4  Lower than normal - indicative of obstructive disease o Restrictive  FEV1 = 2.7 L, FVC = 3 L  Ratio = 0.9  Slightly higher o In pulmonary function tests, want to see if ratios are lower or higher  Inert gas technique ***go over o Can measure lung volume and capacities using inert gas o This is useful for measuring residual volume - what is left in lungs after maximum expiration o Person is hooked up to spirometer but there is 10% helium in the spirometer - person breaths in helium o Come to equilibrium - helium does not get taken into blood; is not soluble  The inert gas technique o Start with helium in spirometer - person is breathing from atmosphere - flip 3-way valve and person breathes helium in o Concentration of helium in lungs becomes equivalent to that in spirometer o This is where dilution comes from - all helium initially present in spirometer is now diluted into gas in the lungs and spirometer  Person is taking air in and out of spirometer  The inert gas technique o Have a spirometer called volume 1 with all the helium in it o After equilibration period, have dilute helium. Concentration is the same throughout the lungs and spirometer (concentration 2) o After dilution, concentration of helium is spread over volume of spirometer and volume of lungs (v2) o Before, concentration of helium in spirometer was entirely in V1 - now diluted concentration (c2) is in lungs and spirometer o V2 = initial volume of spirometer x difference in concentrations divided by C2 o C1 V1 = C2 (V1 + V2) o At end of equilibrium, measure amount
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